This invention relates to the improvement in providing transparent, color-neutral, glass window products particularly those used in shielding windows from excessive solar heat gain during warm weather.
Control of the solar energy entering through window areas of a building is important in maintaining comfortable indoor conditions in warm climates. Solar control has been achieved by adding light-responsive colorant materials to the glass. Tinting of glass in this way has disadvantages in production, however, since a long time may be required to change shades More recently, reflecting and absorbing films have been applied to clear glass, to achieve solar control. Reflection of unwanted radiation is more efficient than absorption, since reflection eliminates the radiation completely, whereas part of the absorbed heat is eventually carried into the building.
It has also been proposed in U.S. Pat. No. 3,885,855 to produce solar control films by reactive sputtering of the nitrides, carbides or borides of the metals titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, or tungsten. While effective optical properties were achieved for some of these materials, any large-scale production of architectural glass by the vacuum electrical method of reactive sputtering would be rather slow and expensive.
In U.S. Pat. No. 4,535,000 issued on Aug. 12, 1985, Roy G. Gordon disclosed a rapid process for deposition of transparent solar screens of titanium nitride while avoiding haze and imperfections on the sheet being coated. These improvements in titanium nitride deposition procedures did not avoid some inherent problems in achieving broad acceptance of TiN as a solar-shielding, glass-coating material in such markets as architectural glass. These problems included some susceptibility to mechanical and chemical attack and some limitations with respect to visual characteristics of TiN film, particularly the tendency to show colors in transmission, i.e. the TiN-window product as normally viewed by building occupants from inside.
Titanium-silicide-type coatings had previously been considered for use as a coating on glass. For example, Varapath in U.S. Pat. No. 4,696,834 describes a TiSi.sub.2 on glass as having a silvery reflection. It is one of the many dozens of films Varapath suggested or investigated in describing a new CVD process. Also, Gross in U.S. Pat. No. 3,885,855 mentions silicides and, inferentially as part of Group IV Periodic Table, titanium silicide for solar coatings. Neither of these parties recognized any particular value to the properties of titanium-silicide coatings with respect to such films as titanium nitride coatings.
In general, it is fair to say that those investigators of the prior art, and others too, have failed to find anything about TiSi.sub.2 coatings which would make it a particularly desirable commercial coating for windows and qualitatively differentiate it from comparable solar-shielding coatings such as the TiN coatings described in U.S. Pat. No. 4,535,000 to Gordon.
In fact, however, and as described below, the present inventor has discovered that the composite properties of certain TiSi.sub.2 -coated glass products make them unique in solar-shielding applications. In particular, they have been found to be advantageous in transmitted appearance over the previously-favored titanium nitride films.
Another type of solar-control window, one based on coatings of fluorine-doped tin oxide, is disclosed in Gordon's U.S. Pat. Nos. 4,265,974 and 4,146,657. Such tin oxide coatings are particularly valuable when high solar transmission and very low emissivity is desired, i.e. when one wishes to reduce winter heating costs. The windows of the present invention have lower solar transmission as well as low emissivity, and are preferred for many applications when economic air-conditioning of a building is an important factor.
It is to be noted that the art cited in this "background section" has necessarily been cited using the present invention as a guide in collection and interpretation of said prior art. It is not to be inferred that such diverse art would be collected without use of the invention described herein as a guide for such collection.